(1) Field of the Invention
The present invention relates to a ballast tamping tool for attachment to a reciprocating tamping drive of a ballast tamping machine, which comprises a shaft having an axis and an upper end affixed to the tamping drive, a tamping blade detachably mounted on a lower end of the shaft, the tamping blade having a ballast tamping front surface, an opposite rear surface and an upper edge between the surfaces, and a plug-in, form-fitting connection for detachably connecting the tamping blade to a lower end of the shaft and defining a recess. The plug-in connection comprises a plug projecting from the lower shaft end and a connecting part at the rear tamping blade surface form-fittingly connecting the tamping blade to the plug.
Ballast tamping tools are used in the tamping heads of mobile tampers for railroad track maintenance or rehabilitation and such tamping tools are affixed to reciprocatory and vibratory drives, and the tools are immersed in the cribs of the ballast bed to tamp ballast under adjacent ties. The immersion of the tamping tools into the ballast and their reciprocation and vibration in the ballast during each tamping cycle subjects the tools to considerable stresses due to the resistance the tools encounter during their immersion, particularly in partially encrusted ballast beds, and the pressures to which the tools are subjected as they compact the ballast under the ties. This causes the tamping blades to be worn very rapidly, and the tamping tools must be removed from their holders on the tamping head drives after a certain operating time to repair the tamping blades. Since the tamping tools are made of metal, they are quite heavy and their replacement, therefore, is quite cumbersome and time-consuming, particularly since the usual tamping heads at each track rail have from four to eight tamping tools, thus requiring the dismounting of 8 to 16 tools on machines designed for the tamping of a single tie during each tamping cycle and up to 32 tamping tools on machines designed for tamping two adjacent ties simultaneously. In addition to the cumbersome and time-consuming dismounting and mounting of the tamping tools, the repair of the tamping blades itself involves expensive and time-consuming work, which furthermore can be repeated only a few times, after which the tamping blade quality is too poor for effective use of the tamping blades. Therefore, as pointed out in the introductory paragraph hereinabove, it has been proposed to use ballast tamping tools with detachable tamping blades whose detachment from, and attachment to, the tool shafts is relatively simple and can be effected rapidly with relatively little effort. (2) Description of the Prior Art
German Pat. No. 2,723,551, published Sept. 25, 1980, discloses a ballast tamping tool with a separable tool shaft and tamping blade, the tamping blade having an affixing stub or bracket forming a plug-in connection with the lower end of the tool shaft. In one embodiment, the tamping blade stub extends into a form-fitting recess in the lower tool shaft end, and in another embodiment, the tamping blade bracket has a recess into which a plug projecting from the lower shaft end form-fittingly fits. The tamping blade stub or bracket and the lower shaft end or plug have bores which are aligned when the tamping blade and shaft are plugged together, and the aligned bores receive a radially yielding connecting element. The tamping blade stub or bracket extend far above the upper edge of the tamping blade so that the plug-in connection is relatively weak and subject to breakage under the operating stresses to which the tool is subjected.
In an effort to overcome this disadvantage, German patent application No. 2,849,951, published May 29, 1980, proposes a two-part ballast tamping tool with a plug-in connection which comprises a first connecting part extending almost to the middle of the shaft and a second connecting part extending from the upper edge of the tamping blade, the two connecting parts interlocking in a complex manner so that the tool is difficult to manufacture and accordingly uneconomical. Furthermore, the radially yielding clamping sleeve or the clamping bolt used to connect the two parts often jams during assembly or disassembly.
U.S. Pat. No. 3,729,055, dated Apr. 24, 1973, discloses a two-part ballast tamping tool wherein a conical projection extends from the upper edge of the tamping blade and is received in a corresponding conical recess in the lower end of the shaft. In this way, the tamping blade may be plugged into the shaft and the two parts are fixed in position by a lock screw or bolt. While this structure is very simple, the connection cannot absorb the powerful forces to which the tool is subjected, particularly a rotation of the tamping blade with respect to the shaft. More particularly, the diameter of the conical projection is too small to prevent breakage of the tool at the connection during the tamping operation.
Austrian Pat. No. 378,797, published Feb. 15, 1985, also discloses a ballast tamping tool with a tamping blade which may be detached from the tool shaft. The lower shaft end of this tool has a trapezoidal cross section and fits into a corresponding tamping blade recess defined between two flanges integral with the tamping blade and inclined with respect to each other. This trapezoidally form-fitting plug-in connection is supposed to provide a friction fit sufficient to hold the two tool parts together without any additional connecting elements. However, in actual tamping operations it has been found that the tamping blade often remains in the ballast and is detached from the shaft when the tamping tools are raised at the end of a tamping cycle. In addition, the preparation of the trapezoidal lower shaft end for a form-fit in the recess defined between the two tamping blade flanges requires special surfacing, which is expensive and, therefore, makes the tools uneconomical. Actually, a similar but simpler trapezoidal plug-in connection between a tamping blade and a tool shaft was proposed in the hand tamping tool disclosed in U.S. Pat. No. 376,565, dated Jan. 17, 1888.